1. Field of the Invention
The present invention relates to a liquid discharge head for applying thermal energy to liquid for generating a bubble therein thereby discharging the liquid, and a head cartridge and a liquid discharge apparatus having such liquid discharge head, and more particularly a liquid discharge head provided with a movable member capable of movement utilizing the bubble generation, and a head cartridge and a liquid discharge apparatus having such liquid discharge head.
In the present invention, xe2x80x9crecordingxe2x80x9d means providing a recording medium not only with a meaningful image such as a character or graphic but also with a meaningless image such as a pattern.
2. Related Background Art
In the recording apparatus such as a printer, there is already known so-called bubble jet recording method, or an ink jet recording method in which for example thermal energy is given to liquid ink contained in a flow path to generate a bubble therein, and the ink is discharged from a discharge port by an action force based on a rapid volume change resulting from such bubble generation and is deposited on a recording medium to form an image. The recording apparatus utilizing such bubble jet recording method is generally provided, as disclosed in the U.S. Pat. No. 4,723,129, with a discharge port for discharging ink, a flow path communicating with the discharge port, and an electrothermal converting member constituting energy generation means for discharging ink contained in the flow path.
Such recording method, being capable of recording a high quality image at a high speed with a low noise level and also of arranging the discharge ports for ink discharge at a high density in the recording head for executing such recording method, has various advantages such as ability to recording an image of a high definition with a compact apparatus and to record a color image easily. Such bubble jet recording method is recently employed in various office equipment such as a printer, a copying apparatus, a facsimile apparatus etc. and even to industrial systems such as a print dyeing apparatus.
With such spreading of application of the bubble jet technology, there are being generated various requirements as explained in the following.
For obtaining an image of high quality, there are proposed a driving condition for realizing a liquid discharge method capable of providing a high ink discharge speed and achieving satisfactory ink discharge based on stable bubble generation, and an improved shape of the flow path for obtaining a liquid discharge head with a high liquid refiling speed into the flow path, in view of the high speed recording.
In addition to such head structures, the Japanese Patent Application Laid-Open No. 6-31918 takes into consideration a backward wave (pressure generated in a direction opposite to the direction toward the discharge port) and discloses a liquid discharge head of a structure capable of preventing the backward wave causing an energy loss at the ink discharge. In the liquid discharge head disclosed in the above-mentioned patent application, a triangular portion of a triangular plate-shaped member is positioned opposed to the heater for generating the bubble. In such liquid discharge head, the backward wave is temporarily and slightly suppressed by the plate-shaped member, but the relationship between the bubble growth and the triangular portion of the plate-shaped member is not at all disclosed nor considered, so that the above-mentioned liquid discharge head has the following drawbacks.
In the above-mentioned patent application, the shape of the liquid droplet cannot be stabilized since the heater is positioned in the bottom of a recess and is not in linear communication with the discharge port and the bubble growth from a side of the triangular plate-shaped member to the entire other side since the bubble growth is permitted from the vicinity of the apex of the triangular portion, whereby the bubble executes ordinary growth in the liquid as if the plate-shaped member is not present. Consequently the presence of the plate-shaped member does not affect at all the growth bubble. Inversely, since the plate-shaped member is entirely surrounded by the bubble, the liquid refill to the heater position at the bottom of the recess generates a random flow at the contraction of the bubble, thereby resulting in accumulation of small bubbles in the recess and disturbing the liquid discharge principle itself based on the bubble growth.
On the other hand, the EP laid-open No. 436047A1 discloses an invention of alternately opening a first valve for intercepting a path between an area in the vicinity of the discharge port and a bubble generating portion and a second valve for intercepting a path between the bubble generating portion and an ink supply portion (cf. FIGS. 4 to 9 in the EP laid-open No. 436047A1). In such invention, however, since only two of the three chambers are separated at a time, the ink discharged following the ink droplet forms a large trailing, whereby a satellite dots considerably increase in comparison with the ordinary liquid discharge method executing the bubble growth, bubble contraction and bubble vanishing. This is presumably because the effect of meniscus retraction by the vanishing of bubble cannot be utilized. Also at the liquid refilling, the liquid is supplied to the bubble generating portion by the bubble vanishing, but cannot be supplied to the area in the vicinity of the discharge port until a next bubble is generated, so that such liquid discharge head not only shows a large fluctuation in the discharged liquid droplet but also has a very low response frequency of liquid discharge, thus being not in the practical level.
The present applicant has made various proposals on a liquid discharge head different completely from the aforementioned liquid discharge head and having a movable member capable of effectively contributing to the liquid discharge droplet (for example a plate-shaped member of which a free end is positioned closer than the fulcrum thereof to the discharge port). Among such proposals, the Japanese Patent Application Laid-Open No. 9-48127 discloses a liquid discharge head capable of limiting the upper limit of displacement of the aforementioned movable member, in order to prevent a slight aberration in the behavior of such movable member. Also the Japanese Patent Application Laid-Open No. 9-323420 discloses a liquid discharge head in which the position of a common liquid chamber, formed at the upstream side of the aforementioned movable member, is shifted to the free end side thereof, namely to the downstream side, utilizing the advantage of the movable member, thereby improving the refilling ability.
As a liquid discharge head in which the displacement of the movable member is limited as disclosed in the aforementioned Japanese Patent Application Laid-Open No. 9-48127, the present applicant proposed a configuration in which a stopper, positioned close to the movable member displaced by the bubble generation, is provided so as to protrude from a position on an internal wall of the flow path and opposed to the free end side portion of the movable member, wherein the displacement of the movable member is limited by such stopper. In such liquid discharge head, however, when the movable member is displaced upward by the bubble generation in the liquid on the heater and approaches a contact plane with the movable member, the approaching speed of the movable member to the stopper is lowered by the presence of a liquid layer therebetween, thereby causing a liquid movement toward the upstream side in the flow path and deteriorating the response speed of the movable member.
The object of the present invention is to provide a liquid discharge head having a stopper as a limiting portion on the internal wall of a liquid flow path for limiting the displacement of a movable member, provided in the flow path, within a desired range, the liquid discharge head being capable of suppressing the movement of the liquid toward the upstream side in the flow path and preventing the loss in the response speed of the movable member when the movable member approaches the stopper by the bubble generation in the liquid contained in the flow path, thereby providing stable recording quality, and a head cartridge and a liquid discharge apparatus having such liquid discharge head.
The above-mentioned object can be attained, according to the present invention, by a liquid discharge head comprising a heat generating member for generating thermal energy for generating a bubble in the liquid, a discharge port constituting a portion for discharging the liquid, a liquid flow path communicating with the discharge port and including a bubble generating area for generating the bubble in the liquid, a movable member provided in the bubble generating area and adapted to displace with the growth of the bubble, and a limiting portion for limiting the displacement of the movable member within a desired range and adapted for discharging the liquid from the discharge port by the energy at the bubble generation by the heat generating member, wherein the limiting portion is provided opposed to the bubble generating area of the liquid flow path, and the movable member displaced by the bubble growth comes into a substantial contact with the limiting portion to separate the upstream side and the downstream side of the liquid flow path thereby forming a substantially closed state by the movable member and the limiting portion, and at least either of the surfaces of the movable member and the limiting portion is formed as a surface with irregularities.
According to the present invention, there is also provided a liquid discharge head comprising a heat generating member for generating thermal energy for generating a bubble in the liquid, a discharge port constituting a portion for discharging the liquid, a liquid flow path communicating with the discharge port and including a bubble generating area for generating the bubble in the liquid, a movable member provided in the bubble generating area and adapted to displace with the growth of the bubble, and a limiting portion for limiting the displacement of the movable member within a desired range and adapted for discharging the liquid from the discharge port by the energy at the bubble generation by the heat generating member, wherein the limiting portion is provided opposed to the bubble generating area of the liquid flow path, and the movable member displaced by the bubble growth comes into substantial contact with the limiting portion to separate the upstream side and the downstream side of the liquid flow path thereby forming a substantially closed state by the movable member and the limiting portion, and at least either of the surfaces of the movable member and the limiting portion is provided with a first exhaustion accelerating structure for exhausting the liquid, present in an area between the movable member and the limiting portion prior to the contact of the movable member and the limiting portion, to the exterior of such area.
More specifically, the first exhaustion accelerating structure is irregularities formed on at least either of the surfaces of the movable member and the limiting portion, where the movable member displaced by the bubble growth and the limiting portion come into substantial contact.
Preferably there is further comprised a side limiting portion of which at least a part comes into substantial contact with a side portion of the movable member displaced by the growth of the bubble.
Preferably there is further comprised a second exhaustion accelerating structure, on at least either of the surfaces of the movable member and the limiting portion, where the movable member displaced by the bubble growth and the limiting portion come into substantial contact, for exhausting the liquid present in an area between the movable member and the side limiting portion prior to the contact of the movable member and the side limiting portion, to the exterior of such area.
Preferably, the second exhaustion accelerating structure is irregularities formed on at least either of the surfaces of the movable member and the side limiting portion, where the movable member displaced by the bubble growth and the side limiting portion come into substantial contact.
Preferably the irregularities of the first and second exhaustion accelerating structures are constituted by forming a groove on the surface having such irregularities, and more preferably the irregularities are comb-tooth shaped. More preferably such irregularities of comb-tooth shape is constituted by forming plural grooves, extending along the direction of the liquid flow path, on the surface having such irregularities. More preferably, such plural grooves have a same length and are arranged in a zigzag manner in a direction perpendicular to the liquid flow path in such a manner that the two neighboring grooves have mutually different longitudinal positions.
Preferably the irregularities are constituted by forming island-shaped projections on the surface having the irregularities, or a recessed portion of the irregularities is constituted by a hole, of which an aperture end is preferably formed on a surface different from the surface having the irregularities.
According to the present invention described above, the limiting portion for limiting the displacement of the movable member within a desired range and the movable member come into substantial contact to separate the upstream side and the downstream side of the liquid flow path thereby forming a substantially closed state by the movable member and the limiting portion, and at least either of the surfaces of the movable member and the limiting portion is formed as a surface with irregularities and is provided with the first exhaustion accelerating mechanism, whereby the liquid present in the area between the limiting portion and the movable member at the approaching thereof to the limiting portion can be rapidly exhausted to the exterior of the area through the recessed portion of the irregularities. Also when the movable member is separated from the limiting portion, the liquid can be supplied to the area therebetween through the recessed portion of the irregularities. Consequently, at the displacement of the movable member, there is reduced the resistance to the movable member by the liquid layer present between the limiting portion and the movable member. Thus, at the displacement of the movable member toward the limiting portion by the bubble generation in the bubble generating area by the thermal energy from the heat generating member, there is shortened the time required by the movable member to contact the limiting portion. Such shortened time required by the movable member for contacting the limiting portion allows to suppress the liquid movement toward the upstream side in the flow path, thereby reducing the loss of bubble generating energy of the heat generating member. Also in case the movable member displaces in a direction farther from the limiting portion from a state a state where the movable member is in contact with or close to the limiting portion, there is also shortened the time required by the movable member for returning to the original position from the contact state with the limiting portion, and there can be prevented the deterioration in the response speed (response frequency) of the movable member. Furthermore, in the liquid discharging operation from the discharge port, there is suppressed the liquid movement to the upstream side in the liquid flow path, whereby the variation of the meniscus can be suppressed and the stable recording quality can be obtained from a low driving frequency to a high driving frequency.
Also in case the above-described liquid discharge head further comprises the side limiting portion of which at least a part comes into substantial contact with the side portion of the movable member displaced by the bubble growth, irregularities constituting a second exhaustion accelerating structure is formed on at least either of the surfaces of the movable member and the limiting portion, where the movable member and the limiting portion come into substantial contact, whereby the liquid present in the area between the limiting portion and the movable member at the approaching thereof to the limiting portion, prior to the contact thereof, can be exhausted to the exterior of the area. Also when the movable member is separated from the limiting portion, the liquid can be supplied to the area therebetween through the recessed portion of the irregularities. Consequently, at the displacement of the movable member, there is reduced the resistance to the movable member by the liquid layer present between the limiting portion and the movable member.
Also the head cartridge of the present invention comprises a liquid discharge head of any of the aforementioned configurations, and a liquid container for holding the liquid to be supplied to the liquid discharge head.
Also the liquid discharge apparatus of the present invention comprises a liquid discharge head of any of the aforementioned configuration, and drive signal supply means for supplying a drive signal for causing the liquid discharge head to discharge liquid.
Also the liquid discharge apparatus of the present invention comprises a liquid discharge head of any of the aforementioned configuration, and recording medium conveying means for conveying a recording medium for receiving the liquid discharged from the liquid discharge head.
Such liquid discharge apparatus executes recording by discharge liquid from the liquid discharge head and depositing the liquid onto the recording medium.